A review on graphene oxide: 2D colloidal molecule, fluid physics, and macroscopic materials

Graphene oxide (GO), a mostly known oxidized derivative of graphene, which possesses two-dimensional (2D) topological nature and good dispersity in multiple common solvents as a single layer, has shown unique molecular science and fluid physics. Assembling 2D GO macromolecules into a variety of carbonaceous architectures is recognized as an important nanotechnology to address the challenge of translating the unprecedented mechanical, electrical, and thermal properties of graphene into a macroscopic level. To realize real-world applications of graphene-based materials, sophisticated architecture manipulation spanning from the nanoscale, mesoscale to macroscale is essential to make sure every atom is at the right place. It takes comprehensive understanding of the compositional chemistry, fluid physics, and solid-state physics of 2D GO and graphene. Much effort in studying the graphene solid-state materials has helped people build perspectives on their structure-property relations. Nevertheless, the molecular science and fluid physics of GO that governs the single molecular behavior and collective effects of sheets still lack exploration. Single GO sheet exhibits both colloid behaviors and molecule conformations, which can be viewed as a 2D colloidal macromolecule with special dynamic aggregate and transition behaviors in solvents. Focusing on this topic, we have summarized recent progress in the science, technology, and engineering of 2D GO colloidal macromolecules with particular focus on intriguing features of molecular conformation, lyotropic liquid crystal, slow relaxation behavior, reversible fusion and fission, etc. Novel solvation-triggered hydroplastic processing for graphene-based macroscopic materials will be introduced, followed by the structural principles for high-performance graphene macroscopic materials. Finally, we will wrap up the topic with some perspectives on future research directions and give our opinions on the roadmap toward graphene industrialization.